SOFIA, Bulgaria (AP) — Unknown artists have painted a Soviet Army monument in Sofia pink in honor of the anniversary of the Prague Spring.

Residents of the capital discovered Wednesday morning that the figures of Soviet soldiers had been brightly colored. An inscription in Bulgarian and Czech below read “Bulgaria apologizes.”

On Aug. 21, 1968, armies of five Warsaw Pact countries — the Soviet Union, Poland, Hungary, Bulgaria and East Germany — invaded Czechoslovakia to crush democratic reforms known as the Prague Spring. The invaders killed 108 people while 500 were seriously injured.

Bulgaria, which marched in lockstep with the Soviet Union for decades, was the first country to insist on the invasion and the last one to formally apologize for its participation — in 1990.